Effects of atrial and brain natriuretic peptides upon cyclic GMP levels, potassium transport, and receptor binding in rat astrocytes

The ability of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) to alter cyclic GMP levels and NaKCl cotransport in rat neocortical astrocytes was determined. At concentrations of 10(-9)-10(-6) M, rat ANP99-126 (rANF), rat ANP102-126 (auriculin B), and rat ANP103-126 (atriopeptin III) stimulated 6- to 100-fold increases in cyclic GMP levels. Porcine BNP (pBNP) and rat BNP (rBNP) were 20%-90% as effective as rANF over most of this concentration range, although 10(-6) M pBNP produced a greater effect than rANF. NaKCl cotransport as measured by bumetanide-sensitive 86Rb+ influx was not altered by exposure of astrocytes to 10(-6)M rANF, pBNP, or rBNP. Both pBNP and rBNP, as well as rat ANP103-123 (atriopeptin I) and des[gl18, ser19, gly20, leu21, gly22] ANF4-23-NH2 (C-ANF4-23) strongly competed for specific 125I-rANF binding sites in astrocyte membranes with affinities ranging from 0.03 to 0.4 nM, suggesting that virtually all binding sites measured at subnanomolar concentrations of 125I-rANF were of the ANP-C (ANF-R2) receptor subtype. These receptors are thought to serve a clearance function (Maack et al.: Science 238:675-678, 1987) and may be linked to a guanylate cyclase activity that is chemically and pharmacologically distinct from that coupled to ANP-A (ANF-R1) receptors (Féthiere et al.: Mol Pharmacol 35:584-592, 1989). ANP receptors on astrocytes may function in limiting the access of ANP and BNP to neurons involved in body fluid and cardiovascular regulation.